Aggregation Hotspots

Transcription

1 Photo: Mike Brittain Aggregation Hotspots George L. Hunt, Jr. School of Aquatic and Fishery Sciences University of Washington

2 Aggregation Hotspots Predictable in Time and Space Places with high rates of trophic transferforaging areas Productivity-driven hotspots Biophysically-forced retention hotspots Conservation significance Spatial and temporal scales Predictability Proportion of population present

3 Hotspots for Trophic Transfer Two major classes of mechanisms Heightened Productivity Prey behavior working against physical gradients Many different spatial and temporal scales Whole sub-arctic compared to sub-tropical Pacific Ocean- not very informative Mesoscale Regions of heightened productivity Oceanic frontal systems Tidal fronts and rips Scale of study depends on organism & question

4 Productivity-driven Hotspots North Water Polynya Sensible heat polynya Opens early, early bloom, large zoops Supports several million dovekies St. Lawrence Island Polynya, Bering Sea Latent heat polynya Strong pelagic-benthic coupling Important area for sea ducks and walrus

5 Okhostk Sea Polynyas Lead polynyas on Arctic shelves St-Lawrence Island Polynya Cape Bathurst polynya Northeast Water North Water Slide courtesy of Martin Fortier

6 Distribution of Dovekies on the water NOW, May 1988 May 1998 Dovekie ind. km Slide courtesy of N. Karnovsky

7 95, ,920 mt C in phytoplankton to support little auks in May! dovekies ind. km May 98 Seawifs image by Simon Belanger and Pierre LaRouche Karnovsky, et al., 2006

8 Retention-Forced Hotspots Require source from which prey advected to be long-lasting Prey behavior works against physical gradient Many sources of gradients Light Density Depth preferences Convergence- with need to stay high Divergence- with need to stay low Eddies

9 Examples of Retention-forced Hotspots Least Auklets at King Island- Convergence Least Auklets at St. Lawrence Is.- Density Auklets at Delarof Is. Convergence and Divergence Shearwaters at Unimak Pass- Convergence, upwelling and Depth-light

10 Location of Delarof Islands

11 Distribution of Auklets on a single crossing of Delarof Pass

12 Distribution of Modes for Three Species of Auklets Delarof Pass

13 Prey Distribution

14 Correlation between Auklet numbers and Convergence rates

15 Examples of Retention-forced Hotspots Least Auklets at King Island- Convergence Least Auklets at St. Lawrence Is.- Density Auklets at Delarof Is. Convergence and Divergence Murres at St. George Is. Depth/Light Shearwaters at Unimak Pass- Convergence, upwelling and Depth-light

16 Predator Aggregations Photo: Mike Brittain With 2-4 birds m -2, this flock contained 4-9 million shearwaters ~ % of the world population

17 Prey Concentrations Shearwaters and Krill Unimak Pass, June 2002 N S Surface view of euphausiid aggregation 0 (m) Seafloor 140 Courtesy of D. Hyrenbach & J. Jahncke

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25 Aggregation Hotspots Spatial and temporal scale dependent on process causing hotspots Habitat preferences- Sea temperature (important for necton- fish, squid, not covered) Production related hotspots lag production to allow development of food web May be quite large in area- warm region May be long-lasting Depend on bio-physical coupling forcing bottom up processes Retention-forced prey aggregations May be very small in area- a fine-scale hotspot Prey produced elsewhere Prey behavior vs gradient- results in concentration Locations often highly predictable

26 Aggregation Hotspots Predictable though not necessarily Stable in Time and Space Places with high rates of trophic transferforaging areas Significant proportion of local or World population What is Significant? If destroyed, what would be considered a significant impact at the population level? Places of major conservation importance

27 Vulnerability to Climate Change Vulnerability of physical mechanisms- Advective processes often dependent on wind patterns Productivity-drivers very sensitive to change Vulnerability of prey organisms- Life history traits sensitive to changes in phenology Physiology sensitive to changes in temperature Prey food availability sensitive to increased stratification

28 Predator Aggregations Photo: Mike Brittain Shearwaters feeding with ~ 100 humpback whales.